Membrane switches are typically constructed of upper and lower plastic films spaced from one another with the two facing surfaces of the films carrying a conductive circuit, which may be printed in conductive ink or applied by vacuum metalizing techniques. The circuits include conductive contacts defining switch cells and conductive tracks leading from each cell to an edge of the films for connection to external circuitry. The films are generally spaced from one another by a die-cut plastic film spacer or an adhesive layer applied in a pattern including apertures. An aperture of the film or adhesive spacer layer is positioned at each switch cell so as to maintain the elements thereof out of contact with each other in a normally nonactivated condition. A switch cell is activated by depressing the upper film so that its switch element contacts a switch element on the other film to thereby form a closed circuit. A membrane switch will generally have an array of switch cells connected to appropriate drive and sense circuitry that enable the detection of a specific cell that is activated. This type of membrane switch is referred to herein as a closed-contact structure since the contacts of the switch are covered by the plastic films used in its construction; thus the upper film of the switch covers the circuit on the lower film of the switch.
This invention is directed to an open-contact type of membrane switch element, meaning that the contact at each switch cell is exposed, which is designed for use with a keyboard that has one or more keys each having a contact on its inboard end. A principal objective in the development of this invention was to provide an efficient membrane switch element for this type of keyboard, another was to provide a new construction for a membrane switch element for such use, and still another was to provide useful methods for the manufacture of the membrane switch elements. Other principal objects were to provide a low cost construction and to reduce the manufacturing costs required to produce the construction.
These and other features, objectives and advantages of the present invention will become apparent from the description which follows that, in connection with the accompanying drawings, sets forth several embodiments of the invention.